1. Field of the Invention
This invention relates to a system for long distance transmission of signals in both directions, particularly for street traffic signaling systems which operate on a time multiplex basis.
2. Description of the Prior Art
My earlier application, Ser. No. 293,019, was directed to such a system for street traffic signaling which, in particular, utilized pulse trains whose digit values could be fixed by timers and synchronizing pulses by way of a control channel. As explained in that application, with conventional time division multiplex methods, a timer is started at each receiving location by a starting or synchronizing pulse, and is thus turned with the timer in a main station. It is therefore possible to apply pulse trains for the transmission of signals from the main station to the individual receiving stations, and from the receiving stations to the main station. However, in order to provide time multiplex transmission functions in an orderly manner, the timer in the receiving station must be accurately synchronized with the timer in the main station and, in particular, the individual widths of the pulses may not change in order to avoid mistakes during transmission. With the increasing usage of computers in the main station, for example, the required pulse train for transmission of control signals can advantageously be obtained from the outputs of such computers. The transmission speed of the individual pulse trains in the computers is extremely high so that the long distance transmission systems which usually operate slowly can therefore be simply operated. However, there still exist the possibility that the computer has not completed its program and that the individual pulses cannot be transmitted at the correct pulse rate.
As mentioned above, in a conventional time multiplex method, a timer is started or synchronized at each receiver by a starting or synchronizing pulse, and is therefore synchronized with the timer in the main or central station. It is therefore possible to transmit a plurality of signals from the central station to the individual stations, and from the individual stations to the central station by way of a few circuits or one single circuit. In addition to the possibility that a computer has not completed its program and cannot therefore emit the individual pulses at the correct rate, another drawback of the prior systems is the requirement for a large number of timers in the individual stations which renders the system more expensive and susceptible to interference.